package org.bouncycastle.util.encoders;

/**
 * <p>
 * Title: BASE64Decoder
 * </p>
 * <p>
 * Description: BASE64Decoder
 * </p>
 * <p>
 * Copyright: Copyright (c) 2009
 * </p>
 * <p>
 * Company: ND
 * </p>
 * 
 * @author: Jason.Lee
 * @version: 1.0
 */
public class BASE64Decoder {
	private char[] source;
	private int length, length2, length3;
	private int blockCount;
	private int paddingCount;

	public BASE64Decoder() {

	}

	public BASE64Decoder(char[] input) {
		int temp = 0;
		source = input;
		length = input.length;

		for (int x = 0; x < 2; x++) {
			if (input[length - x - 1] == '=')
				temp++;
		}
		paddingCount = temp;

		blockCount = length / 4;
		length2 = blockCount * 3;
	}

	public byte[] decode() {
		byte[] buffer = new byte[length];
		byte[] buffer2 = new byte[length2];

		for (int x = 0; x < length; x++) {
			buffer[x] = char2sixbit(source[x]);
		}

		byte b, b1, b2, b3;
		byte temp1, temp2, temp3, temp4;

		for (int x = 0; x < blockCount; x++) {
			temp1 = buffer[x * 4];
			temp2 = buffer[x * 4 + 1];
			temp3 = buffer[x * 4 + 2];
			temp4 = buffer[x * 4 + 3];

			b = (byte) (temp1 << 2);
			b1 = (byte) ((temp2 & 48) >> 4);
			b1 += b;

			b = (byte) ((temp2 & 15) << 4);
			b2 = (byte) ((temp3 & 60) >> 2);
			b2 += b;

			b = (byte) ((temp3 & 3) << 6);
			b3 = temp4;
			b3 += b;

			buffer2[x * 3] = b1;
			buffer2[x * 3 + 1] = b2;
			buffer2[x * 3 + 2] = b3;
		}

		length3 = length2 - paddingCount;
		byte[] result = new byte[length3];

		for (int x = 0; x < length3; x++) {
			result[x] = buffer2[x];
		}

		return result;
	}

	private byte char2sixbit(char c) {
		char[] lookupTable = new char[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G',
				'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
				'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e',
				'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q',
				'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2',
				'3', '4', '5', '6', '7', '8', '9', '+', '/' };
		if (c == '=')
			return 0;
		else {
			for (int x = 0; x < 64; x++) {
				if (lookupTable[x] == c)
					return (byte) x;
			}

			return 0;
		}

	}

}
